As is well known, abnormalities in the human eye can lead to vision impairment. Some typical abnormalities include variations in the shape of the eye, which can lead to myopia (near-sightedness), hyperopia (far-sightedness) and astigmatism as well as variations in the tissue present throughout the eye, such as a reduction in the elasticity of the lens, which can lead to presbyopia. A variety of technologies have been developed to try and address these abnormalities, including corneal implants.
Corneal implants can correct vision impairment by altering the shape of the cornea. Corneal implants can be classified as an onlay or an inlay. An onlay is an implant that is placed over the cornea such that the outer layer of the cornea, e.g., the epithelium, can grow over and encompass the implant. An inlay is an implant that is surgically implanted into the cornea beneath a portion of the corneal tissue by, for example, cutting a flap in the cornea and inserting the inlay beneath the flap. Both inlays and outlays can alter the refractive power of the cornea by changing the shape of the anterior cornea, by having a different index of refraction than the cornea, or both. Since the cornea is the strongest refracting optical element in the human ocular system, altering the cornea's anterior surface is a particularly useful method for correcting vision impairments caused by refractive errors. Inlays are also useful for correcting other visual impairments including presbyopia.